Photographic image reduction method

ABSTRACT

CONTINUOUS TONE IMAGES ARE OPTIONALLY CONVERTED TO HALF TONE IMAGES OF A REDUCED SIZE THAT IS CONVENIENT FOR USE IN STORAGE AND RETRIEVAL SYSTEMS. THE QUALITY AND TONAL GRADATIONS OF THE ORIGINAL CONTINUOUS TONE IMAGE ARE MAINTAINED IN THE REDUCED HALF TONE FILM RECORD. WHEN DESIRED, THIS REDUCED HALF TONE RECORD OF ORIGINAL CONTINUOUS TONE IMAGE, MAY BE RECONSTITUTED BY SUITABLE OPTICAL AND/OR PHOTOGRAPHIC MEANS TO OBTAIN AN EYE READABLE IMAGE OF THE ORIGINAL SUBJECT MATTER.

United States Patent 3,589,899 PHOTOGRAPHIC IMAGE REDUCTION METHODSeymour L. Hersh, Freehold, N.J., assignor to the United States ofAmerica as represented by the Secretary of the Army No Drawing. FiledMay 22, 1968, Ser. No. 731,313 Int. Cl. G03f 5/00; G03c 11/00 US. Cl.96-45 3 Claims ABSTRACT OF THE DISCLOSURE Continuous tone images areoptically converted to half tone images of a reduced size that isconvenient for use in storage and retrieval systems. The quality andtonal gradations of the original continuous tone image are maintained inthe reduced half tone film record. When desired, this reduced half tonerecord of original continuous tone image, may he reconstituted bysuitable optical and/or photographic means to obtain an eye readableimage of the original subject matter.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates in general, to theart of microphotography, and in particular to a method of reducing thesize of continuous tone images while maintaining image quality and tonalgradations.

The subject of micro-recording or reduction of line copy material formicro filming use is a well established science. Equipment, materialsand techniques exist that enable an experienced operator to reduce linecopy (black and white) material as much as 300 times. The materials usedinclude copy film such as commercially available Eastman Kodak HighResolution Plates or micro file material. In both cases the images whendeveloped as rec ommended are very high contrast. This very highcontrast, though desirable in line work, is a serious disadvantage incontinuous tone recording. That is, the small latitude of the highcontrast film makes it impractical to record the wide range of tonesthat are inherent in continuous tone images.

Accordingly, the general object of this invention is to provide a methodof reducing the size of continuous tone images while maintaining imagequality and tonal gradations using a high contrast, high resolutionfilm. A more particular object of this invention is to provide such amethod wherein the resulting recorded image can be reconstructedoptically and/or photographically to provide duplicate copies of theoriginal stored continuous tone information or visual presentation ineye readable form.

SUMMARY OF THE INVENTION The method of the invention involves thefollowing:

(a) A conventional continuous tone image either positive or negative, isscreened by photographhic means, using the finest screen available.

(b) This half tone image is now optically reduced and recorded on highcontrast, high resolution film.

(c) When desired, the recorded image is then optically restored toprovide eye readable copy or photographically reproduced to providepermanent copies of the stored continuous tone information. The limitingsize of the enlarge- 3,589,899 Patented June 29, 1971 ments reproducedfrom the micro images stored on film, will be determined by the screenpattern used. The limit will be reached when the reconstructedphotograph loses the quality of being a continuous image and appears asa dot pattern when viewed with the unaided eye.

The half tone image may also be prepared using micro recording materialwith a screen built in (auto-screen). Such materials are presentlyavailable for conventional half tone applications. In this instanceimage reduction would be performed in a subsequent operation. Thecontinuous tone image may be screened by contact printing or during thereduction process.

DESCRIPTION OF THE PREFERRED EMBODIMENT If the imagery to bemicrophotographed is a positive reflection copy, such as an 8" X 10photograph having good tonal range, a preferred method of approach is asfollows:

The print is mounted on a copy board having a vacuum back and/ or glassplaten to provide an extremely flat copy surface. Illumination of thecopy must be uniform and non-glaring such as to prevent reflections onthe image surface from deteriorating the quality of the copy. Theimagery is then copied at a 2 to 1 reduction ratio using a copy cameraof the type used in graphic arts process work such as the Chempcographic arts process camera, and Kodalith, ortho film which is a graphiclow speed, fine grain orthochromatic sensitive film. The copy film isused in conjunction with a negative magenta contact screen having 200lines per inch. The resulting product when processed in lithographichigh contrast developer such as E. K. Kodalith Developer is a 4" X 5"screen half tone negative containing a 200 line per inch pattern.

This screened half tone negative is now microphotographed usingequipment such as Borrowdale Miniaturization Camera using a reductionratio of 10 to l which results in a reduced positive half tone recordcontaining approximately 2000 lines per inch. This practical limit isestablished by the resolution of the film used for microphotography.

The choice of positive or negative original copy, positive or negativeintermediates, positive or negative half tones and positive or negativereductions would depend upon availability of materials and the type ofend product desired. For reproduction purposes a micro record negativeis desirable, for direct projection viewing a micro record positive isdesirable. The method used would be only a modification of the preferredembodiment. Al though the preferred embodiment describes a contactscreen of 200 lines per inch, an operator skilled in the art can chooseappropriate screens and appropriate reduction ratios of both copyprocedures to provide the desired micro record that is within thepractical limit of resolution of the film used.

The method of the invention as herein described is also consideredapplicable for use as a means of producing micro motion pictures whereinthe images are contained on a narrow web of film or a cylinder of film.

The foregoing is to be considered merely as illustrative of theinvention and not in limitation thereof.

What is claimed is:

1. A method of reducing the size of continuous tone images whilemaintaining image quality and tonal gradations so that the reducedcontinuous tone images are suitable for microrecording use, said methodincluding the steps of (A) screening the continuous tone image with acontact screen of 200 lines per inch to obtain a half tone ReferencesCited image no larger in size than the original continuous tone UNITEDSTATES PATENTS image, and (B) optically reducing the half tone image ata reduction ratio of 10 to 1 to obtain a reduced half tone 1,155,1289/1915 Burgess 96 45 record containing approximately 2000 lines perinch.

2. A method according to claim 1 wherein the contin- 5 DAVID KLEINPnmary Exammer uous tone image is a positive image. U S C1 X R 3. Amethod according to claim 1 wherein the continuous tone image is anegative image.

